I think I've only ever heard zone 1 & 2 called together once in recent memory, and that was a flight that was a US outstation to YYZ earlier this year that was maybe a third full and the sum total of zones 1 & 2 were me and some other guy.
I think part of the issue is the gates that have zone 1 & 2 lines together. They've pretty much fixed that at YOW but it seems to be a problem at a lot of YYZ gates, especially for the smaller flights. If you're going to enforce the zones, signs enforcing the zones help.